Sizing device, polishing apparatus, and polishing method

ABSTRACT

A sizing device in a polishing apparatus for measuring a thickness of a wafer in course of polishing by laser beam interference, includes: a light-source for irradiating the wafer in course of polishing with a laser beam, a light-receiving portion for receiving reflected light from the wafer in course of polishing irradiated with the laser beam from the light-source, a calculating part for calculating a measured value of the thickness of the wafer in course of polishing irradiated with the laser beam based on the reflected light received through the light-receiving portion. The calculating part can calculate the wafer thickness in course of polishing by calculating a measuring error value of the wafer thickness in course of polishing from resistivity of the wafer in course of polishing based on a previously determined correlation between wafer resistivity and measuring error value of wafer thickness, and by compensating the measuring error value.

TECHNICAL FIELD

The present invention relates to a sizing device, a polishing apparatus,and a polishing method.

BACKGROUND ART

With the progress of miniaturization and layer-increasing ofsemiconductor devises, polishing technologies such as Double SidedPolishing (DSP) have been an essential technology for production processof semiconductor devises.

In DSP for flattening, one of the important specification is in-planeuniformity (flatness) of finished thickness of a substrate. To improvethe in-plane uniformity of finished thickness, it is important tocontrol the finished thickness accurately. Accordingly, polishingapparatuses with a sizing device have been used for accuratelymonitoring the thickness of wafer in course of polishing (e.g., seePatent Document 1).

With increasing requirement for the in-plane uniformity (flatness) of asubstrate in finished thickness, the sizing comes to be required to haveaccuracy of about ±0.1 μm or less, or even higher accuracy in recentyears.

The devices that have been used for controlling the finished thicknessinclude an eddy current sizing device, a sizing device to measure thedistance to the upper face of carrier, and a sizing device using laserbeam interference.

By the sizing apparatus to measure the distance to the upper face ofcarrier, however, the required sizing accuracy of about ±0.1 μm cannotbe secured. When the eddy current sizing device is compared with thelaser interferometric sizing device, the latter laser interferometricsizing device is superior in view of limitation of setting environmentand measuring accuracy.

Accordingly, the laser interferometric sizing device has come to bewidespread. The laser interferometric sizing device has become anessential technology particularly for highly accurate processing of a P−or P+ substrate. That is, the laser interferometric sizing device hasbecome an essential technology to improve the uniformity of finishedthickness in polishing such as DSP. The resistivity is commonly 10 Ω·cmor more in P− substrate, more than 0.01 Ω·cm and less than 10 Ω·cm in P+substrate, and 0.01 Ω·cm or less in P++ substrate, particularly in thisdescription.

In recent years, it becomes necessary to cope with high flatness also inthe P++ substrate with lower specific resistance, and the laserinterferometric sizing device has been reexamined. Hereinafter, themechanism of laser interferometric sizing device will be described withexemplifying a double-side polishing apparatus.

In a laser interferometric sizing device, laser beam for interferencepierces a hole formed to penetrate the turn table of the double-sidepolishing apparatus. In polishing of a substrate, the substrate isrotated and revolved by rotation of a gear that is engaged with acarrier, and the foregoing hole is formed on a position where the orbitsof rotation and revolving of the substrate pass. Accordingly, the laserinterferometric sizing device allows laser beam to pierce through thishole to irradiate the substrate in course of polishing with the laserbeam, and allows the reflected light from the front and back surfaces ofthe substrate to be introduced into a light-receiving portion almostsimultaneously.

These signals are introduced as digital signals and are recognized asinformation of the thickness of the substrate by using a Fouriertransformation. In this case, the signals of the reflected light fromthe back surface of substrate can be introduced sufficiently from P− andP+ substrates, but the reflected light becomes weak in P++ substrates.

FIG. 6 shows a relation between resistivity of wafer (thickness of 775μm) and transmittance of laser beam. The laser beam used forconventional sizing device has a wavelength of about 1300 nm, and thetransmittance at this wavelength is about 50% in P− substrate, but onlyabout 1% in P++ substrate.

Accordingly, measurement of the thickness of P++ substrate can beachieved by increasing the output of laser beam to about twice as muchas in measuring the thickness of P− substrate and by setting the optimalregion of the frequency. As described above, highly accurate sizing hasbecome possible with the laser interferometric sizing device by changingthe wavelength and intensity of laser beam.

In this way, it becomes possible to obtain thickness data not only in P−substrates and P+ substrates but also in P++ substrates, which havelower resistivity, by optimizing output of laser beam and signals usedfor a Fourier transformation.

CITATION LIST Patent Literature

Patent Document 1: Japanese Unexamined Patent Application Publication(Kokai) No. H11-285956

SUMMARY OF INVENTION Technical Problem

In continuous polishing of a substrate, however, it becomes frequent toobserve phenomena in which required accuracy of sizing cannot bemaintained depending on a group (lot) of substrates to be polished.There has been a problem that accuracy of sizing cannot be secured inthe first batch after changing a lot, particularly in polishing of asubstrate with low resistivity, thereby often failing to obtain anintended thickness of the substrate.

Accordingly, after changing a polishing lot of substrates, the intendedthickness has been adjusted by a method in which a difference from theintended thickness is calculated from the first finished thickness ofthe substrate polished at the first polishing batch in the lot, and thedifference from the intended thickness is taken into account inprocessing of the next polishing batch to maintain the accuracy ofpolishing.

In this method, however, the test processing to determine a differencefrom the intended thickness after changing a lot causes lowering of theyield and increase of the production cost.

As described above, there have been problems that the required accuracyof sizing sometimes cannot be maintained depending on the lot ofsubstrates polished in a continuous polishing, and the yield is lowereddue to test processing performed in every alteration of the lot todecrease the difference from an intended thickness that is caused bylowering of accuracy of polishing.

The present invention was accomplished in view of the above-describedproblems. It is an object of the present invention to provide a sizingdevice that can prevent accuracy of polishing from lowering to give highaccuracy in continuous polishing when a lot of substrates to be polishedis changed.

The present invention also aims to provide a polishing method that cangive a substrate with slight difference from the intended thicknesswithout necessity of test processing of a substrate by preventing theaccuracy of sizing from lowering due to alteration of a lot ofsubstrates to be polished.

Solution to Problem

To solve the problems described above, the present invention provides asizing device provided in a polishing apparatus for polishing a surfaceof a wafer for measuring a thickness of the wafer in course of polishingwith the polishing apparatus in which the wafer brought into slidingcontact with a polishing pad pasted on a turn table, and the thicknessof the wafer is measured by laser beam interference, comprising:

a light-source for irradiating the wafer in course of polishing with alaser beam,

a light-receiving portion for receiving reflected light from the waferin course of polishing irradiated with the laser beam from thelight-source,

a calculating part for calculating a measured value of the thickness ofthe wafer in course of polishing irradiated with the laser beam based onthe reflected light received through the light-receiving portion,

wherein the calculating part is capable of calculating the thickness ofthe wafer in course of polishing by calculating a measuring error valueof the thickness of the wafer in course of polishing from resistivity ofthe wafer in course of polishing based on a previously determinedcorrelation between wafer resistivity and measuring error value of waferthickness, with the measured value being corrected for the measuringerror value.

In the inventive sizing device, a measuring error of wafer thickness ina sizing device can be calculated from resistivity of a wafer in courseof polishing based on correlation between wafer resistivity andmeasuring error value of wafer thickness. Accordingly, the measuringerror can be compensated depending on the resistivity when the lot ofwafers to be polished is changed during continuous polishing to changeresistivity of wafer to be polished, whereby the actual thickness of awafer in polishing can be measured with high accuracy.

It is preferable that the calculating part be capable of correcting thethickness of the wafer in course of polishing for the measuring error bydetermining an offset value for cancelling the measuring error in themeasured value from the resistivity of the wafer in course of polishingbased on the correlation between wafer resistivity and a measuring errorvalue of wafer thickness, with the offset value being added to orsubtracted from the measured value.

As described above, the actual thickness of a wafer in polishing can bemeasured with high accuracy, more specifically, by compensating themeasuring error with the offset value to cancel the measuring error ofthickness of a wafer in polishing in the way described above.

The resistivity of the wafer in course of polishing can be a valuedetermined from resistivity at the both ends of an ingot from which thewafer in course of polishing have been cut out and resistivity of aportion of the ingot from which the wafer in course of polishing havebeen cut out.

In this way, the resistivity of wafer in polishing can be easilydetermined in each substrate.

It is preferable that the correlation between wafer resistivity and ameasuring error value of wafer thickness be based on each of thepolishing apparatus.

The correlation between wafer resistivity and measuring error value ofwafer thickness can slightly differ depending on polishing apparatus.Accordingly, the accuracy of sizing can be further improved by using theforegoing correlation in each polishing apparatus.

It is preferable that the resistivity of the wafer be 0.01 Ω·cm or less.

The inventive sizing device can be favorably used for measuring athickness of low-resistance wafer the resistivity of 0.01 Ω·cm or lessin particular.

To achieve the foregoing objects, the present invention also provides apolishing apparatus comprising any of the sizing device described above.

In such a polishing apparatus, a thickness of wafer in course ofpolishing can be calculated accurately, and a wafer can be obtained withslight difference from an intended thickness thereby. In addition, testpolishing for calculating difference from an intended thickness is notnecessarily required, and the yield can be improved thereby.

To achieve the foregoing objects, the present invention also provides apolishing method including a step of polishing a surface of a wafer bybringing the wafer into sliding contact with a polishing pad pasted on aturn table; wherein the wafer is polished while measuring a thickness ofthe wafer in course of polishing by using a sizing device by which thethickness of the wafer in course of polishing is measured by laser beaminterference, and the polishing is stopped when the measured value ofthe thickness of the wafer in course of polishing measured by using thesizing device becomes a prescribed value, comprising:

a step of deriving a correlation between wafer resistivity and measuringerror value of wafer thickness to previously determine the correlationbefore the step of polishing;

wherein the wafer is polished while calculating the thickness of thewafer in course of polishing in the step of polishing by calculating ameasuring error value of the thickness of the wafer in course ofpolishing from resistivity of the wafer in course of polishing based onthe correlation between wafer resistivity and measuring error value ofwafer thickness, with the measured value of the thickness of the waferin course of polishing being corrected for the measuring error value.

In the inventive polishing method, a measuring error of a sizing devicein wafer thickness can be calculated from resistivity of the wafer incourse of polishing, together with the correlation between waferresistivity and a measuring error value of wafer thickness. Accordingly,when a lot of wafers to be polished is changed to change the resistivityof wafer to be polished in continuous polishing, the measuring error canbe compensated depending on the resistivity, and a wafer with slightdifference from an intended thickness can be obtained thereby. Inaddition, test polishing for calculating difference from an intendedthickness is not necessarily required in each alteration of a lot ofwafers, and the yield can be improved thereby.

In the inventive polishing method, it is preferable that the thicknessof the wafer in course of polishing be corrected for the measuring errorvalue by calculating an offset value for cancelling the measuring errorvalue in the measured value of the thickness of the wafer in course ofpolishing measured by using the sizing device from the resistivity ofthe wafer to be polished based on the correlation between waferresistivity and measuring error value of wafer thickness, with theoffset value being added to or subtracted from the measured value of thethickness of the wafer in course of polishing.

In this way, the measuring error of wafer thickness in course ofpolishing can be compensated, more specifically, by cancelling themeasuring error with the offset value.

It is preferable that the inventive polishing method further comprise astep of test polishing previous to the step of deriving a correlation,wherein a plurality of test wafers with different resistivity arepreviously subjected to test polishing while measuring thicknesses ofthe test wafers by using the sizing device, and the correlation betweenwafer resistivity and a measuring error value of wafer thickness isdetermined in the step of deriving a correlation on the basis of thethicknesses of the test wafers after the test polishing.

In this way, the correlation between wafer resistivity and a measuringerror value of wafer thickness can be obtained as a concrete form of thepresent invention.

The resistivity of the wafer to be polished can be determined fromresistivity at the both ends of an ingot from which the wafer to bepolished have been cut out and resistivity of a portion of the ingotfrom which the wafer have been cut out.

In this way, the resistivity of wafer to be polished can be obtainedeasily in each substrate.

It is preferable that the correlation between wafer resistivity andmeasuring error value of wafer thickness be determined on the basis ofeach of the polishing apparatus.

The correlation between wafer resistivity and a measuring error value ofwafer thickness sometimes differs in each polishing apparatus.Accordingly, the accuracy in sizing can be improved by using theforegoing correlation of each polishing apparatus.

It is preferable that the resistivity of the wafer to be polished be0.01 Ω·cm or less.

The inventive polishing method can be favorably used for polishing alow-resistance wafer with the resistivity of 0.01 Ω·cm or less inparticular, while measuring the thickness thereof.

Advantageous Effects of Invention

In the present invention, high accuracy of sizing can be obtained bypreventing lowering of accuracy in sizing due to alteration of a lot ofsubstrates to be polished, and a substrate with slight difference froman intended thickness can be obtained thereby. In addition, testpolishing of a substrate is not necessarily required, and the yield canbe improved thereby.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic sectional view showing an example of a sizingdevice, together with polishing apparatus provided with the sizingdevice according to the present invention;

FIG. 2 is a chart showing a relation between resistivity of test waferand a measuring error value in a measured value of thickness of testwafer determined in Example;

FIG. 3 is a chart showing relation between resistivity of wafer and ameasuring error value in a measured value of wafer thickness determinedin Example;

FIG. 4 is a chart showing results of polishing wafers in Example;

FIG. 5 is a chart showing results of polishing wafers in ComparativeExample;

FIG. 6 is a chart showing relation between resistivity and transmittanceof laser beam in substrates.

DESCRIPTION OF EMBODIMENTS

Hereinafter, the embodiments of the present invention will be described,but the present invention is not limited thereto.

As described above, there have been a problem that accuracy of sizingvaries due to alteration of a lot of wafers to be polished, causing thepolished wafer to have a thickness with larger difference from anintended thickness.

The present inventors have diligently investigated to solve the forgoingproblem to found that resistivity of wafer has a correlation with ameasuring error value of wafer thickness. The inventors have conceivedto calculate a wafer thickness more accurately by correcting it with themeasuring error on the basis of this correlation and resistivity ofwafer to be polished, thereby completing the present invention.

First, a sizing device and a polishing apparatus provided with thesizing device according to the present invention will be described byreference to FIG. 1. FIG. 1 shows an example of a double-side polishingapparatus provided with the inventive sizing device. As shown in FIG. 1,the inventive sizing device 1 can be installed in the double-sidepolishing apparatus 10.

As shown in FIG. 1, the double-side polishing apparatus 10 is providedwith the upper turn table 11 and the lower turn table 12 that areprovided upward and downward facing with each other, and each of theturn tables 11 and 12 is pasted with the polishing pad 13. Between theupper turn table 11 and the lower turn table 12, the sun gear 14 isprovided at the central part, and the circular internal gear 15 isprovided at the peripheral part. The wafers W are held in holding holesof the carrier 16 and are interposed between the upper turn table 11 andthe lower turn table 12.

The sun gear 14 and the internal gear 15 each have a teeth portionengaged with corresponding teeth of the outer circumferential gear ofthe carrier 16, which enables the carrier 16 to revolve around the sungear 14 while rotating, interlocking with the upper turn table 11 andthe lower turn table 12 being rotated by an actuator, which is not shownin the figure. At this time, the wafer W, held in the holding hole ofthe carrier 16, is brought into sliding contact with the upper and lowerpolishing pads 13, and the both surfaces are polished simultaneouslythereby. Incidentally, the wafer W is supplied with slurry from anozzle, which is not shown in the figure, in polishing of the wafer W.

The inventive sizing device 1 applies laser beam interference to measurethe thickness of water in course of polishing with the polishingapparatus as shown in FIG. 1. This sizing device 1 is provided with thelight-source 2 for irradiating the wafer W with a laser beam in courseof polishing by using such a double-side polishing apparatus 10 asdescribed above, the light-receiving portion 3 for receiving reflectedlight from the wafer W in course of polishing, and the calculating part4 for calculating a measured value of the thickness of the wafer W incourse of polishing on the basis of the reflected light. As shown inFIG. 1, the incident light into the wafer W and the reflected light fromthe wafer W pierce the hole 17 provided in the upper turn table 11.

In the inventive sizing device 1, the calculating part 4 is capable ofcalculating the thickness of the wafer W in course of polishing bycalculating a measuring error value of the thickness of the wafer incourse of polishing from resistivity of the wafer W in course ofpolishing based on previously determined correlation between waferresistivity and a measuring error value of wafer thickness, and bycompensating the measuring error value.

More specifically, the calculating part 4 is capable of compensating themeasuring error of the thickness of the wafer in course of polishing bydetermining an offset value for cancelling the measuring error in themeasured value from the resistivity of the wafer in course of polishingbased on the correlation between wafer resistivity and a measuring errorvalue of wafer thickness, with the offset value being added to orsubtracted from the measured value.

To perform this series of operations effectively, it is desirable to usea terminal such as a personal computer (PC) as the calculating part 4.By introducing a PC, it becomes possible to acquire data from adatabase, and to automatically perform a series of operations such asautomatic acquisition of resistivity data of a wafer to be polished,calculation of the offset values, and addition or subtraction of thecalculated offset values to measured values.

Subsequently, the inventive polishing method will be described byreference to the double-side polishing apparatus 10 provided with theinventive sizing device 1 shown in FIG. 1.

The inventive polishing method includes a step of deriving acorrelation, in which the correlation between wafer resistivity and ameasuring error value of wafer thickness is previously determined beforethe step of polishing the wafer W.

The correlation can be determined by the following, for example. First,a test polishing step is previously performed, in which a plurality oftest wafers with different resistivity are each subjected to testpolishing while measuring the thicknesses of the test wafers with thesizing device, before the step of deriving a correlation. In the testpolishing, the polishing is stopped when the measured value of thethickness of the test wafer by using the sizing device becomes anintended value.

Then, the intended thickness set in the test polishing and the actualthickness of the polished test wafer are recorded. The difference ofthese values are used for calculating a measuring error value of themeasured value of thickness of test wafer in the test polishing. In thetest polishing, the inventive sizing device 1 may be used as the sizingdevice. At this stage, however, the measuring error is not compensatedin the measured value of thickness of test wafer since the foregoingcorrelation is not determined yet.

Subsequently, the step of deriving a correlation is performed. In thisstep, the correlation between wafer resistivity and a measuring errorvalue of wafer thickness can be determined from the data of measuringerror of wafer thickness occurred in the test polishing and resistivityof the wafer.

For example, each [measuring error] is determined by calculating ([anactual thickness of test wafer]−[an intended thickness]) on the basis ofpolishing data of wafers with various resistivity recorded in the stepof test polishing and is plotted in relation to [resistivity of testwafer] to give a relation of measuring error in terms of resistivitythrough the least squares method. As the examples, FIGS. 2 and 3 showcorrelations between resistivity and a measuring error value determinedin Example that will be described later. It can be seen from FIG. 3, inparticular, that the [measuring error] and the [resistivity of testwafer] give a regression line with high correlation. In this way, it ispossible to derive the correlation between wafer resistivity and ameasuring error value of wafer thickness.

It is preferable to determine the correlation between wafer resistivityand measuring error value of wafer thickness on the basis of each of thepolishing apparatus. In the relation of wafer resistivity and measuringerror value of wafer thickness, the slope and the intercept can vary ineach polishing apparatus provided with a sizing device. Accordingly, thecorrelation is preferably determined in each polishing apparatus tocalculate the measuring error highly accurately. Since the correlationmay be influenced by the polishing conditions, constant renewal of therelation can further improve the accuracy of sizing.

Then, the step of polishing wafer W is performed. In the polishing step,the polishing is performed while measuring the thickness of the wafer incourse of polishing by using a sizing device by which the thickness ofthe wafer in course of polishing is measured by laser beam interference.The polishing is stopped when the measured value of the thickness of thewafer in course of polishing measured by using the sizing device becomesa prescribed value.

In the polishing step of the present invention, measuring error value ofthe thickness of the wafer in course of polishing is calculated fromresistivity of the wafer in course of polishing based on the correlationbetween wafer resistivity and measuring error value of wafer thicknessdetermined in the step of deriving a correlation. The wafer is polishedwhile calculating the thickness of the wafer in course of polishing bycompensating the measuring error value.

More specifically, the measuring error can be compensated as follows.First, an offset value is calculated for cancelling the measuring errorvalue in the measured value of the thickness of the wafer, which ismeasured by using the sizing device in course of polishing, from theresistivity of the wafer to be polished based on the correlation betweenwafer resistivity and measuring error value of wafer thickness as shownin FIG. 3.

The resistivity of the wafer to be polished can be determined fromresistivity at the both ends of an ingot from which the wafer to bepolished have been cut out and resistivity of a portion of the ingotfrom which the wafer have been cut out, for example. The resistivity ofan ingot is always measured before cutting out (slicing) a wafer, andthe resistivity at the both ends of the ingot can be easily obtainedthereby. In an ingot produced by CZ pulling method, segregationphenomenon occurs during the pulling, thereby making it possible toeasily determine the resistivity at each portion by using the distancefrom the end of the ingot. Accordingly, the resistivity of a wafer to bepolished can be easily determined in each of substrates which aredefined in the order of slicing.

Then, the measuring error is cancelled using the calculating part 4, bywhich the offset value is added to or subtracted from the measured valueof the thickness of the wafer in course of polishing. This enables theactual thickness of wafer to be calculated with high accuracy.

As described above, in the present invention, a measuring error valueoccurred in the main polishing can be calculated from the resistivity ofa wafer to be polished based on the correlation between waferresistivity and measuring error value of wafer thickness, and the actualthickness of the wafer in course of polishing can be calculated withhigh accuracy by measuring the thickness of the wafer in course ofpolishing while compensating the measuring error. Accordingly, testprocessing is not necessarily required, and polishing can be performedwith slight difference between an intended thickness and a finishedthickness. The present invention also makes it possible to decrease thedifference of a finished thickness from an intended thickness to about±0.1 μm or less, or further smaller value, even in polishing of a lowresistance wafer with the resistivity of 0.01 Ω·cm or less such as a P++substrate in particular.

EXAMPLE

Hereinafter, the present invention will be described more specificallyby showing Example of the present invention and Comparative Example, butthe present invention is not limited to this Example.

Example

A plurality of silicon wafers with the diameter of 300 mm werecontinuously polished by the inventive polishing method using thedouble-side polishing apparatus 10 provided with the sizing device 1 asshown in FIG. 1. The polishing agent was colloidal silica with theaverage particle size of 35 to 70 nm, containing potassium hydroxideadded thereto, diluted with pure water to have a pH of 10.5. As thepolishing pads, commercially available non-woven fabric type was used.

First, a plurality of P++ test silicon wafers with various resistivity(the resistivity of 7.2 to 9.3 mΩ·cm) were subjected to continuous testpolishing by using the double-side polishing apparatus 10 shown inFIG. 1. As the calculating part 4, a PC was used. This PC was connectedto the double-side polishing apparatus 10 to manage the input record ofactual finished thicknesses of wafers, intended thicknesses, offsetvalues, and resistivity. The laser beam used in the sizing device wasinfrared wavelength-tunable laser with a wavelength of 1300 nm and anoutput of 10 mW or more.

The relation between change of resistivity of test wafer and measuringerror (the difference of a finished thickness from an intendedthickness) in the test polishing is shown in FIG. 2. As can be seen fromFIG. 2, high correlation is found between the resistivity of wafer andthe measuring error.

Subsequently, the step of deriving a correlation was performed. In thisstep, each [measuring error] is determined by calculating ([an actualthickness of test wafer]−[an intended thickness]) on the basis ofpolishing data recorded in the step of test polishing and is plotted inrelation to [resistivity of test wafer] to give correlation of measuringerror of wafer thickness in terms of resistivity of the wafer throughthe least squares method. The obtained correlation between [measuringerror] and [resistivity of test wafer] is shown in FIG. 3. As can beseen from FIG. 3, a regression line with high correlation was obtained.

Then, the step of polishing was performed. In this step, wafers withdifferent resistivity for each lot (the resistivity of 5 to 10 mΩ·cm)were polished. The offset value was calculated as follows. When the lotwas changed to introduce a substrate having different resistivity by 1mΩ·cm in this double-side polishing apparatus, it was found that themeasuring error value differed by about 0.2035 μm depending on thechange of resistivity based on the relation shown in FIG. 3, that is[measuring error (μm)]=0.2035×[resistivity (mΩ·cm)]−1.7343. Thefollowing considers a case in which a silicon wafer with resistivity of8.5 mΩ·cm is polished (in this case, the [offset value]=0 on the basisof the relation shown in FIG. 3), and then a silicon wafer of the nextlot having resistivity of 9.5 mΩ·cm after compensating the measuringerror, for example. In the polishing of the silicon wafer withresistivity of 9.5 mΩ·cm, the offset value is increased by 0.2035 μmfrom that of the preceding lot in which a wafer with resistivity of 8.5mΩ·cm is polished. That is, it is assumed that the [offset value]=0.2035μm. In polishing the silicon wafer with resistivity of 9.5 mΩ·cm, themeasuring error can be cancelled by subtracting the offset value of0.2035 μm from the measured value, and the wafer with differentresistivity can be provided with the same finished thickness. When asilicon wafer with resistivity of 9.5 mΩ·cm is polished, and then asilicon wafer with resistivity of 7.5 mΩ·cm in the next lot is polished,for example, the offset value is decreased by 0.4070 μm from that of thepreceding lot in which a wafer with resistivity of 9.5 mΩ·cm ispolished. That is, it is assumed that the [offset value]−0.2035 μm. Inpolishing the silicon wafer with resistivity of 7.5 mΩ·cm, the measuringerror can be compensated by subtracting the offset value of −0.2035 μmfrom (adding 0.2035 μm to) the measured value, and the same finishedthickness can be obtained as in the foregoing.

The resistivity of wafer to be polished had been measured before cuttingout the substrate and was recorded in a data base of the PC (thecalculating part 4), together with the lot information. The calculatingpart 4 had been provided with a program to call data of lot informationand resistivity before polishing to calculate an offset valueautomatically from the difference between resistivity of wafer to bepolished and resistivity of wafer in the preceding lot. In Example,polishing was performed while altering the offset value based on theresistivity of wafer to be polished when changing the lot by using sucha program. When such a program is installed in the calculating part 4,it is possible to sufficiently cope with an alteration of an intendedthickness.

FIG. 4 shows a distribution of difference between intended thickness andfinished thickness of wafer that was continuously polished as describedabove. As shown in FIG. 4, the differences from intended values werecontrolled smaller compared to those of Comparative Example that will bedescribed later. It was found that larger proportion of wafers showedthe difference from an intended value that was within ±0.1 μm, inparticular, compared to that of Comparative Example which will bedescribed below. This is because highly accurate sizing could beperformed by appropriately compensating the measuring error of thicknessdepending on alteration of resistivity of wafer when chancing the lot.

Comparative Example

Polishing of silicon wafers with the diameter of 300 mm was performed inthe same condition as in Example except that the sizing device was aconventional sizing device to perform polishing without compensating ameasuring error.

FIG. 5 shows a distribution of difference between intended thickness andfinished thickness of wafer that was polished as described above. Asshown in FIG. 5, the variation of finished thickness became larger, andthe differences from the intended thickness became larger. The ratio ofwafers that showed the difference from an intended value of ±0.1 μm ormore, in particular, was largely increased compared to that of Example.

It is to be noted that the present invention is not limited to theforegoing embodiment. The embodiment is just an exemplification, and anyexamples that have substantially the same feature and demonstrate thesame functions and effects as those in the technical concept describedin claims of the present invention are included is the technical scopeof the present invention.

1-12. (canceled)
 13. A sizing device provided in a polishing apparatusfor polishing a surface of a wafer for measuring a thickness of thewafer in course of polishing with the polishing apparatus in which thewafer is brought into sliding contact with a polishing pad pasted on aturn table, and the thickness of the wafer is measured by laser beaminterference, comprising: a light-source for irradiating the wafer incourse of polishing with a laser beam, a light-receiving portion forreceiving reflected light from the wafer in course of polishingirradiated with the laser beam from the light-source, a calculating partfor calculating a measured value of the thickness of the wafer in courseof polishing irradiated with the laser beam based on the reflected lightreceived through the light-receiving portion, wherein the calculatingpart is capable of calculating the thickness of the wafer in course ofpolishing by calculating a measuring error value of the thickness of thewafer in course of polishing from resistivity of the wafer in course ofpolishing based on a previously determined correlation between waferresistivity and measuring error value of wafer thickness, with themeasured value being corrected for the measuring error value.
 14. Thesizing device according to claim 13, wherein the calculating part iscapable of correcting the thickness of the wafer in course of polishingfor the measuring error value by determining an offset value forcancelling the measuring error value in the measured value from theresistivity of the wafer in course of polishing based on the correlationbetween wafer resistivity and measuring error value of wafer thickness,with the offset value being added to or subtracted from the measuredvalue.
 15. The sizing device according to claim 13, wherein theresistivity of the wafer in course of polishing is a value determinedfrom resistivity at the both ends of an ingot from which the wafer incourse of polishing have been cut out and resistivity of a portion ofthe ingot from which the wafer in course of polishing have been cut out.16. The sizing device according to claim 14, wherein the resistivity ofthe wafer in course of polishing is a value determined from resistivityat the both ends of an ingot from which the wafer in course of polishinghave been cut out and resistivity of a portion of the ingot from whichthe wafer in course of polishing have been cut out.
 17. The sizingdevice according to claim 13, wherein the correlation between waferresistivity and measuring error value of wafer thickness is based oneach of the polishing apparatus.
 18. The sizing device according toclaim 14, wherein the correlation between wafer resistivity andmeasuring error value of wafer thickness is based on each of thepolishing apparatus.
 19. The sizing device according to claim 15,wherein the correlation between wafer resistivity and measuring errorvalue of wafer thickness is based on each of the polishing apparatus.20. The sizing device according to claim 16, wherein the correlationbetween wafer resistivity and measuring error value of wafer thicknessis based on each of the polishing apparatus.
 21. The sizing deviceaccording to claim 13, wherein the resistivity of the wafer is 0.01 Ω·cmor less.
 22. A polishing apparatus comprising the sizing deviceaccording to claim
 13. 23. A polishing method including a step ofpolishing a surface of a wafer by bringing the wafer into slidingcontact with a polishing pad pasted on a turn table; wherein the waferis polished while measuring a thickness of the wafer in course ofpolishing by using a sizing device by which the thickness of the waferin course of polishing is measured by laser beam interference, and thepolishing is stopped when the measured value of the thickness of thewafer in course of polishing measured by using the sizing device becomesa prescribed value, comprising: a step of deriving a correlation betweenwafer resistivity and measuring error value of wafer thickness topreviously determine the correlation before the step of polishing;wherein the wafer is polished while calculating the thickness of thewafer in course of polishing in the step of polishing by calculating ameasuring error value of the thickness of the wafer in course ofpolishing from resistivity of the wafer in course of polishing based onthe correlation between wafer resistivity and measuring error value ofwafer thickness, with the measured value of the thickness of the waferin course of polishing being corrected for the measuring error value.24. The polishing method according to claim 23, wherein the thickness ofthe wafer in course of polishing is corrected for the measuring errorvalue by calculating an offset value for cancelling the measuring errorvalue in the measured value of the thickness of the wafer in course ofpolishing measured by using the sizing device from the resistivity ofthe wafer to be polished based on the correlation between waferresistivity and measuring error value of wafer thickness, with theoffset value being added to or subtracted from the measured value of thethickness of the wafer in course of polishing.
 25. The polishing methodaccording to claim 23, further comprising a step of test polishingprevious to the step of deriving a correlation, wherein a plurality oftest wafers with different resistivity are previously subjected to testpolishing while measuring thicknesses of the test wafers by using thesizing device, and the correlation between wafer resistivity andmeasuring error value of wafer thickness is determined in the step ofderiving a correlation on the basis of the thicknesses of the testwafers after the test polishing.
 26. The polishing method according toclaim 24, further comprising a step of test polishing previous to thestep of deriving a correlation, wherein a plurality of test wafers withdifferent resistivity are previously subjected to test polishing whilemeasuring thicknesses of the test wafers by using the sizing device, andthe correlation between wafer resistivity and measuring error value ofwafer thickness is determined in the step of deriving a correlation onthe basis of the thicknesses of the test wafers after the testpolishing.
 27. The polishing method according to claim 23, wherein theresistivity of the wafer to be polished is determined from resistivityat the both ends of an ingot from which the wafer to be polished havebeen cut out and resistivity of a portion of the ingot from which thewafer have been cut out.
 28. The polishing method according to claim 24,wherein the resistivity of the wafer to be polished is determined fromresistivity at the both ends of an ingot from which the wafer to bepolished have been cut out and resistivity of a portion of the ingotfrom which the wafer have been cut out.
 29. The polishing methodaccording to claim 25, wherein the resistivity of the wafer to bepolished is determined from resistivity at the both ends of an ingotfrom which the wafer to be polished have been cut out and resistivity ofa portion of the ingot from which the wafer have been cut out.
 30. Thepolishing method according to claim 26, wherein the resistivity of thewafer to be polished is determined from resistivity at the both ends ofan ingot from which the wafer to be polished have been cut out andresistivity of a portion of the ingot from which the wafer have been cutout.
 31. The polishing method according to claim 23, wherein thecorrelation between wafer resistivity and measuring error value of waferthickness is determined on the basis of each of the polishing apparatus.32. The polishing method according to claim 23, wherein the resistivityof the wafer to be polished is 0.01 Ω·cm or less.